The invention relates to a film end detector for use in an automatic film winding camera.
A conventional automatic film winding camera includes a film end detector which is in the form of a rotary disc mounted on a drive shaft of a motor which is connected to a film winding mechanism, with a notch of a given width being formed in the disc to permit a mechanical arm to be engaged with or disengaged from the notch to operate a microswitch or the contacts of a reed relay, thus providing a film end detection by the closing or opening or off of the contacts. Specifically, when a film end is not reached, the drive shaft of the motor will rotate through one revolution to wind up a length of the film corresponding to one frame. In this instance, the contacts will cycle from their off condition through their on condition and then return to their off condition again. By contrast, when a film end is reached during the course of a winding operation, the drive shaft cannot rotate through one complete revolution, but ceases to rotate before the one revolution is completed. Consequently, the contacts are only switched from their off to their on condition, and remain on. The failure of the contacts to return to their off condition provides an indication that the film end is reached. However, an angular position detector of this type which is provided with mechanical contacts experiences difficulties in respect of durability. In addition, it disadvantageously requires an increased size.
A conventional film end detector of the type described may malfunction, though with a reduced probability, and a false indication may be given indicating that a length of the film remains even though the full length of the film has been actually exhausted. After investigation, it is found that such a malfunction is attributable to the fact that in the event the disc comes to a stop after the notch formed therein has slightly moved past the arm, the disc rotates in the opposite direction, though slightly, when the motor is deenergized, allowing the arm to engage the notch again. Such a malfunction precludes a normal photographing on the film, and causes an important opportunity to take pictures to be missed. This is of particular significance in taking pictures through a microscope.